In airplanes (termed “aircraft” below), air enriched with nitrogen is conducted into an aviation fuel tank and/or a trim tank to reduce the risk of explosion. Air with a normal oxygen and nitrogen content can create a highly flammable mixture together with aviation fuel vapours. Nitrogen-enriched air is also used in extinguisher systems, in order to smother any fire sources by increasing the nitrogen content, with a resultant reduction in the oxygen content. The nitrogen-enriched air is produced by inerting systems. These are also termed inert gas systems, Inert Gas Generation Systems (IGGS) or On Board Inert Gas Generation Systems (OBIGGS). Cooled bleed air from jet engines or auxiliary turbines (so-called auxiliary power units, APUs) is used as an air source for the inert gas production. However, this bleed air has a temperature of roughly 200° C. and must therefore be cooled to a temperature tolerable for the IGGS. Furthermore, the air supplied to the IGGS must also have a certain pressure, and must be compressed or expanded, therefore. Systems that supply air with these predetermined temperature and pressure characteristics are described as a CSAS (Conditioned Service Air System).
FIG. 1 illustrates a known CSAS, which represents an air supply for an IGGS 100. The bleed air 110 branched off from an engine is supplied to a compressor 120 or even an expansion device. In FIG. 1, a motor-operated compressor 120 is shown, which supplies the bleed air 110 at the pressure required for operating the IGGS 100. Bleed air 110 that has a pressure higher than that required can also be routed past the compressor by a valve 125 and supplied, suitably expanded, to the IGGS. Since the bleed air usually has a temperature that is too high for use in the IGGS 100, or the bleed air 110 is additionally heated by the compressor 120, it has to be cooled with the help of a heat exchanger 130. The bleed air 110 can optionally be pre-cooled before entering the compressor 120 in an upstream heat exchanger 135. For finer control of the temperature required in the IGGS 100, the CSAS comprises a bypass line with a suitable control valve 140. Finally, other regulating elements, such as e.g. regulating valves 150 and 160, are provided in the air lines of the CSAS. An ozone converter 165 can also be optionally integrated, which removes the ozone that is detrimental to the IGGS. The cooling in the heat exchangers 130/135, thus their heat sink, is effected by an air stream. This is produced by outside air, which is made available in flight mode as ram air of a ram air channel 180 and in ground operation by an additional conveying device, such as e.g. a ventilator or blower 170.
The present disclosure has recognized that the tapping of bleed air of an engine and the fitting of ram air channel inlets and outlets in the outer skin of an aircraft entail disadvantages for an IGGS. For example, the tapped bleed air is no longer available to the engine itself, which leads to increased fuel consumption. The fitting of ram air channel openings produces vortices on the outside of the aircraft, which likewise increase the aircraft's fuel consumption.